Investigating internal noise in migraine: a possible mechanism underlying perceptual deficits

[Truncated abstract] Migraine is a common neurological disorder that has been associated with differences in visual processing including poorer detection of motion and form (Antal et al., 2005; Ditchfield, McKendrick, & Badcock, 2005; McKendrick & Badcock, 2004; McKendrick, Badcock, Badcock, & Gurgone, 2006a; McKendrick, Badcock, & Gurgone, 2006b), longer motion after-effects (Shepherd, 2001; Shepherd, 2006), larger tilt after-effects (Shepherd, 2001; Shepherd, Palmer, & Davis, 2002) and decreased contrast sensitivity (Shepherd, 2000; Wagner, Manahilov, Loffler, Gordon, & Dutton, 2010). However the mechanism(s) underlying these processing deficits is (are) still under investigation. Some transcranial magnetic stimulation studies have argued for hyperexcitability in the visual cortex of individuals with migraine (Aurora, Ahmad, Welch, Bdardhwji, & Ramadan, 1998; Battelli, Black, & Wray, 2002; Brighina, Piazza, Danielle, & Fierro, 2002). However, the exact mechanism underlying hyperexcitability is unclear with recent studies arguing for increased excitation of neural mechanisms (Battista, Badcock, & McKendrick, 2010; Huang, DeLano, & Cao, 2006), which may result in increased levels of internal noise. Internal noise can be broken into two components: (i) additive noise which is random neural firings that are unrelated to the presence of a stimulus and (ii) multiplicative noise which is scaled by the range of intensities in the stimulus. External noise methods are one way of estimating the amount of internal noise associated with a particular visual task (Falkenberg & Bex, 2007; Levi, Klein, & Chen, 2007; Pelli, Levi, & Chung, 2004; Pelli & Farell, 1999).